1. Field of Invention
This invention relates to swim fins and more particularly swim fins of an advanced design for swimming and diving at water level and below the water, and more particularly to swim fins employing aerodynamic shapes (hydrodynamic shapes when used in water) attached to the sides of a planar blade and employing an aerodynamic shaped tail fin. By having multiple hydrodynamic shapes in a series with a set distance from one another, the accelerated flow of water produced from the forward hydrodynamic shapes increases the effectiveness of the trailing hydrodynamic shapes through serial amplification of the flow of water over those shapes.
2. Description of Prior Art
Man has long sought means to propel through water with greater comfort, effectiveness, efficiency and speed. Market studies rate competitive and recreational swimming/scuba diving/snorkeling as some of the most popular exercise activities in the US. Swimming along with personal exploration of shallow and deep-sea life environments have traditionally used frog-like swim fins in a paddle-like manner with different relief schemes to lighten the work involved. Merriam-Webster Dictionary defines a swim fin: a flat rubber shoe with the front expanded into a paddle used in skin diving. This definition might better read in broad patent terminology as a means of securing the wearer's foot, generally a foot pocket, to a means of propulsion in the water, generally a blade functioning as a paddle.
Many swim fins in the past have made claims about using a “fish” based system of propulsion for their propulsion strategy. The majority of the exterior shape of a fish is involved with the fish's system of propulsion, and yet earlier conventional swim fins have seldom born any resemblance to the “exterior shape of a fish”. Without using a structure related to the shape of a fish, it is difficult to follow the logic of the claim of “fish” based propulsion. There are two notable examples of “fish” propulsion systems based on the propulsion structure found in the best swimming fish, and they are found in U.S. Pat. No. 6,375,531 and U.S. Pat. No. 6,893,307, both authored by this inventor.
Both of these patents use a planar blade which is similar in function to the stiff forward part of the body of a fish (the rigid forebody) and flexible second part of the body of a fish (the flexible afterbody). The rigid forebody causes water to start flowing when it is moved through the water and the flexible afterbody causes the shaped flow of water over a effective hydrodynamic airfoil similar in shape to the fluke (tail fin) of a whale or caudal fin of a fish when it is placed at a proper angle of attack (self-regulated pitch). This flowing water over the tail fin produces “lift” as additional propulsion without any extra effort from the swimmer/diver.
U.S. Pat. No. 6,375,531, utilizes fish-derived shapes and their hydrodynamic propulsion wherein a swimmer's foot pocket is located on the stiff part of the planar blade of the swim fin beginning around the middle of the foot and extending about six inches beyond the foot (the rigid forebody). Some sort of lengthy stiff portion is common in most swim fins and this extra length increases the amount of work necessary to move the swim fin through the water because of the physics involved in moving weight at a distance involving centrifugal force due to the length of the stiff section. The extra length increases the overall length of the swim fin (usually adding to the cost of manufacturing the swim fin and the difficulty of storage and traveling with a longer swim fin).
Pending patent Ser. No. 10/060,142 teaches a first part of the swim fin, a stiff portion of the planar blade (the rigid forebody), attached to a foot pocket with side scoops used to channel water. The side scoops are not hydrodynamic airfoils. The side scoops do allow for shorter swim fins to be more effective and reduce manufacturing costs while improving storage and travel requirements.
There are earlier patents teaching the use of multiple hydrodynamic airfoils in parallel but they are not following one another in a series. For example, U.S. Pat. No. 5,536,190 and U.S. Pat. No. 4,944,703 teach multiple hydrodynamic airfoils. The airfoils in these patents are parallel in alignment, and hinged without providing self-regulating pitch to the flow of water over the foils making them ineffective by allowing the airfoils to pivot instead of causing useful lift. Since they are not spaced to follow one another, there is no opportunity for an accelerated flow of water over one airfoil to improve the performance of airfoils following in series (serial amplification).
U.S. Pat. No. 6,183,327 teaches a swim fin relating to a hydrodynamic form apparently similar to the tail fin of a whale. The form taught in this patent has several differences of serious consequence differing from a true whale's tail fin. A whale's tail fin reveals an airfoil shape when seen as a cross-section. When the cross-section is taken from the projected perpendicular line oriented to the curve of the leading edge of the whale's tail fin, it is clear that the airfoil changes its orientation to follow the leading edge. By the time it is taken from the distal edge of the tail fin, it is actually facing the side of the tail fin instead of facing the front of the tail fin. U.S. Pat. No. 6,183,327 teaches of an airfoil shape that continuously faces the front of the fin through the tail fin. This would create vortices that are contradictory to the ones found in a whale's tail fin which dramatically reduces vortices on each distal end of the whale's tail fin instead of increasing them as is the case taught in this patent. More importantly, this patent does not teach a method or apparatus for creating a flow of water over the airfoil shape at a proper angle of attack (self-regulating pitch). Without this flow of water over the hydrodynamic airfoil shape, no lift is produced. Simply waving the taught swim fin form in the water will not create any lift because the pitch would not be at the right angle of attack to the flow of water. Without facilitating a flow of water at the proper pitch, there is no useful “lift” produced to aid in propulsion.
U.S. Pat. No. 5,041,039 teaches an amphibious shoe that allows for connection of a diving flipper for use in swimming. This patent does not deal with hydrodynamic shapes to create lift to aid in propulsion. In a similar manner, International Patent WO 01/85266A2 (international publication number which is also the recently issued U.S. Pat. No. 6,620,008) discloses a swim fin with a frontal blade portion having a pair of inflexible side blade portions. This patent does not teach the use of a flexible blade or any hydrodynamic airfoil shapes used to create “lift” to aid in propulsion.
Another form of swimming shoe is taught in U.S. Pat. No. 3,107,372. Here we find another set of stiff blades meant to act as a paddle in the water. This patent does not have a flexible blade, or any hydrodynamic “airfoil” shapes used to create “lift”.
In water, two types of propulsion are possible for swimmers. “Drag” propulsion and “Lift” propulsion. Paddles (most swim fins fall into this category) create propulsion by creating a void in the water into which the water flows. This flowing water pulls the paddle with it into the void. This is “drag” propulsion (the water flowing around the sides of the paddle “drag” the paddle forward into the void).
Certain shapes, most notably airfoil shapes, cause the water to flow more quickly over one surface than flows over the opposite surface producing a negative pressure. This negative pressure, called “lift”, causes the swim fin to move in that direction. The most efficient way of moving through water (and through light fluids such as air) is through “lift”. The great advantage of using lift occurs when the lifting forces passively work by simply holding an airfoil in a moving stream of water at the proper angle of attack with the negative pressures creating proper force vectors. The latest scientific analysis of these forces created by airfoils also includes descriptions of the vortices produced by the swirling water after leaving the airfoil. The proper angle of attack is generally thought to be about 15 to 20 degrees above or below the flow of fluid.
Numerous articles dealing with the science concerning this issue have issued within the last few years. Many of the articles written by Professor Walker at the University of Southern Maine deal with the efficiencies of rowing (the use of paddles for propulsion) versus “flapping” (the use of airfoils for propulsion) in water based upon studies of fish in nature. In these articles, the conclusion was that the proper use of airfoils was always more efficient that using paddles at every speed. Relevant printed content of the sites is included with this patent application:
(Rowing and Flapping at Low Re—Jeffrey A. Walker—American Zoologist, in press) (Printed from the internet on Nov. 2, 2003 for inclusion as documentation.)
(Mechanical performance of aquatic rowing and flying—Jeffrey A. Walker* and Mark W. Westneat—Royal Society—doi 10.1098/rspb.2000.1224) (Printed from the internet on Nov. 2, 2003 for inclusion as documentation.)
(The image describes the OPTIMAL FLAPPING WING CYCLE (with best propulsive efficiency), and below, the cycle of a caudal (movement of a dolphin flipper). (Printed from the internet on Nov. 2, 2003 for inclusion as documentation.)
(bionic analysis: MOVEMENT OF A DOLPHIN FLIPPER —>PROPULSIVE HYDROFOIL). (Printed from the internet on Nov. 2, 2003 for inclusion as documentation.)